Arrangement for runtime compensation of a runtime difference arising through emulation of a high frequency signal

ABSTRACT

An arrangement for runtime compensation of a runtime difference, arising through emulation of a high frequency signal, is disclosed, with a signal x(t), for emulation by a signal processing device, which emulates the signal x(t) with a signal x(t) and a device for determining a difference signal between the signals x(t) and x(t). The arrangement is characterized in that the emulated signal x(t) is conducted via filter with a negative group runtime for certain frequency ranges.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP02/00656 filed on and 23 Jan. 2002 and GermanApplication No. 101 03 812.7 filed on 29 Jan. 2001 and EuropeanApplication No. 011 01 968.4 filed on 29 Jan. 2001, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an arrangement for runtime compensationof a runtime difference arising through emulation of a high frequencysignal.

High frequency signals, transmitted by any transmission systems of alinear or non-linear nature, such as amplifier chains for example, canbe emulated by signal processing devices. One example of a transmissionsystem is set out in the patent application filed by the applicant withthe same application date, relating to a sigma-delta modulator fordigitizing analog high frequency signals. Ideally the signal emulationof the output signal of the transmission system proceeds without a timedelay in relation to the original signal, so that the precisely emulatedsignal components of the emulated signal extinguish the original signalcompletely in a difference signal.

Practical instances of signal emulation however generally result in aruntime difference between the emulated signal and the original signal.As can be clarified below, the time delay of the emulated signal resultsin extinction of the signal components in a certain frequency rangeonly. Here x(t) designates the original output signal of thetransmission system and {circumflex over (x)}(t) the emulated signal; τstands for the runtime difference of the emulated signal.

The following equation appliesx(t)−{circumflex over (x)}(t)≈x(t)−x(t−τ)

X(jω)−_(e) ^(−jωτ) X(jω)=X(jω)·(1−_(e) ^(−jωτ))

In order to achieve broadband signal extinction, runtime elements arecommonly used, which delay the signal x(t) by the period of the runtimedifference τ of signal emulation {circumflex over (x)}(t).x(t−τ)−{circumflex over (x)}(t)≈x(t−τ)−x(t−τ)=0

The highly linear runtime elements used for this are technicallyexpensive due to the high level of spectral purity of the signal x(t)and give rise to high manufacturing costs.

SUMMARY OF THE INVENTION

One possible object of the invention is therefore to create anarrangement for runtime compensation of a runtime difference arisingthrough emulation of a high frequency signal, which allows broadbandsignal emulation and is simple to set up from a technical point of view.

This object may be achieved by an arrangement for runtime compensationof a runtime difference arising through emulation of a high frequencysignal with a signal to be emulated x(t), with a signal processingdevice, which emulates the signal x(t) with a signal {circumflex over(x)}(t), and with a device for determining a difference signal betweenthe signals x(t) and {circumflex over (x)}(t), which is characterized inthat the emulated signal {circumflex over (x)}(t) is routed via a filterwith a negative group runtime for certain frequency ranges. Theparameters of the filter are selected so that the overall transmissionfunction of the difference signal in the required frequency range haszeros or is significantly attenuated. This means that the runtimedifference arising from signal emulation is compensated to the maximumdegree possible in this frequency range.

According to one embodiment of the invention the signal x(t) forms theoutput signal of a transmission signal and a signal u(t) forms the inputsignal of the transmission system. The transmission system here cancomprise an amplifier or even an amplifier chain. However any linear ornon-linear transmission system can be used.

According to a further embodiment of the invention the arrangement has aregulation device, which can be used to modify the emulated signal{circumflex over (x)}(t), so that the difference signal is minimal.

The difference signal for regulating signal emulation is preferablyrouted to the signal processing device.

According to one embodiment of the invention a signal evaluation unit isprovided, which evaluates the difference signal and routes the evaluatedsignal to the signal processing device.

According to a preferred embodiment of the invention, the analog inputsignal for controlling signal emulation is routed to the signalprocessing device.

The filter preferably has runtime elements, which delay the digitalsignal.

A linear filter is preferably used to achieve the object. An FIR, IIR orany other linear filter can for example be used.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is an illustration of a system for signal emulation according tothe related art,

FIG. 2 is an illustration of a system, according to one aspect of theinvention, for signal emulation,

FIG. 3 is an illustration of a further embodiment of a system accordingto the invention for signal emulation,

FIG. 4 is an illustration of an example of the application of the systemaccording to the invention for signal emulation, and

FIG. 5 is an illustration of a second embodiment of a system accordingto the invention for signal emulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout

The arrangement shown in FIG. 1 for signal emulation, as known from therelated art, has an input signal u(t), which is transmitted by anylinear or non-linear transmission system 1. The signal x(t) is presentat the output of the transmission system 1. The signal x(t) is emulatedin the signal processing device 2 with runtime differences, i.e. delays,arising in relation to the signal x(t). The signal {circumflex over(x)}(t) is present at the output of the signal processing device 2. Aruntime element 3 is provided for the signal x(t) to compensate forruntime differences and this delays the signal x(t) for a time τ. Here τis preferably selected so that it corresponds to the runtime differenceproduced by the signal processing device 2. Assuming ideal signalemulation and a delay τ, which corresponds precisely to the signal delayproduced by signal emulation, the following applies for the differencesignal x(t−τ)−{circumflex over (x)}(t) created from {circumflex over(x)}(t) and the delayed signal x(t−τ) for all frequenciesx(t−τ)−{circumflex over (x)}(t)=0

A control loop can be created to improve signal emulation and thistransmits the difference signal, which is usually not equal to 0, to thesignal processing device 2. The delayed signal x(t−τ) can also be usedas a control variable.

With the system there may be no need to use a runtime element tocompensate for the runtime difference. An illustration of the system isshown in FIG. 2.

The emulated signal {circumflex over (x)}(t) is passed as the inputsignal to a linear filter 4. An FIR, IIR or any other linear filter canbe used here. The coefficients of the linear filter are selected so thatfor certain frequency ranges the runtime difference produced by thesignal processing device 2 is compensated for by the linear filter. Incertain frequency ranges the filter used has a negative group runtimebut is still causal and therefore feasible because of positive groupruntimes in other frequency ranges, i.e. signal delays. In this waysignal emulation is achieved in the required frequency range, which is abroader band compared with previous solutions and is simple to set upbecause of the digital filters used. The difference signal formed at thesumming unit 5 can be used as a control variable for the signalprocessing device 2. It is however conceivable for an evaluation resultof the difference signal to be used as the control variable. A signalevaluation unit 6 is used for this and converts the difference signalinto a Taylor series for example. Other types of signal breakdown canalso be used.

A further example of signal breakdown is the spectral analysis (Fourieranalysis) of the difference signal. The object is to minimize the powerof the difference signal within a sub-band. For this it is sufficient tosend to the signal processing device 2 those results of the spectralanalysis of the difference signal, which describe the frequency responsewithin the relevant sub-band.

The power of the error signal (difference signal) within the relevantfrequency band can be used as a further alternative parametric controlvariable.

An embodiment of the invention is described below using an exampleaccording to FIG. 3. In this example an FIR filter 4 a is used toachieve negative group runtime for certain frequency ranges. Runtimecompensation is to be carried out in the low-pass range. The followingis to apply for the delay elements τ′ of the filterτ′=τ,

i.e. the delay elements t′ of the filter each correspond to the runtimedifference t of the signal processing device. The starting point isestablished by a linear filter design with good attenuation at thefrequency ω=0:

$H_{Design} = {1 - {\sum\limits_{l = 1}^{q - 1}\;{a_{l}z^{- l}}}}$

where q=1, 2, 3, . . . and 1=1, 2, 3, . . . .

In this exampleH _(Design)=(1−_(z) ⁻¹)^(ν)

is selected with ν=2 and z=e^(jωτ). The following therefore results atthe output of the summing unit 5 for the difference signal y(t)

$\begin{matrix}{{y(t)} = {{x(t)} + {\sum\limits_{l = 1}^{q - 1}\;{a_{l}{\hat{x}\left( {t - {\left( {l - 1} \right)\tau}} \right)}}}}} \\{= {{{x(t)} - {2{\hat{x}(t)}} + {\hat{x}\left( {t - \tau} \right)}} \approx {{x(t)} - {2{x\left( {t - \tau} \right)}} + {x\left( {t - {2\tau}} \right)}}}}\end{matrix}$

The following follows from the linearity of the Fourier transformation

$\begin{matrix}{{Y\left( {\mathbb{e}}^{j\omega} \right)} = {{\left( {1 - {\mathbb{e}}^{- {j\omega\tau}}} \right)^{2}{X\left( {\mathbb{e}}^{j\omega} \right)}} = {\left( {1 - {2{\mathbb{e}}^{- {j\omega\tau}}} + {\mathbb{e}}^{- {j\omega 2\tau}}} \right){X\left( {\mathbb{e}}^{j\omega} \right)}}}} \\{= {{X\left( {\mathbb{e}}^{j\omega} \right)} - {2\;{\mathbb{e}}^{- {j\omega\tau}}{X\left( {\mathbb{e}}^{j\omega} \right)}} + {{\mathbb{e}}^{- {j\omega 2\tau}}{X\left( {\mathbb{e}}^{j\omega} \right)}}}}\end{matrix}$

corresponds toy(t)=x(t)−2x(t−τ)+x(t+2τ)

The definition of group runtime according to K. D. Kammeyer,Nachrichtenübertragung (Message Transmission), Teubner Stuttgart 1996,is as follows

${\tau_{g}(\omega)} = {- \frac{\mathbb{d}{\phi(\omega)}}{\mathbb{d}\omega}}$

Frequency response of the relevant sub-systemH _(Sub)=2−e ^(−jωτ)

At frequencies ωτ≈2π, _(e) ^(−jω2π)≈1−j (ωτ−2π) (Taylor seriesdevelopment). The following then applies approximatelyH _(Sub)=2−(1−j(ωτ−2π))=1+j(ωτ−2π))

The phase is approximately ωτ−2π, the differential derivation to ωresults in negative values: −τ is the group runtime to be compensated.

Therefore the coefficients α₁ . . . α_(n) are selected as follows forthe filter shown: α₁=2, α₂=−1 and α₃ . . . α_(n)=0.

A specific example of the application of the invention is shown in FIG.4. A cascade stage of an analog-digital converter system with a low-passsigma-delta modulator 7 is shown, which is the subject of a furtherpatent application by the applicant. The digital signal emulation of theanalog input signal u(t) is achieved here byf the low-pass sigma-deltamodulator 7. The two output signals of a signal processing device 2 a,result from the multiplication of the input signal u(t) and a sin or cossignal and are designated as inphase or quadrature components, arecombined again to form a signal in the digital mixer 8 and thenconverted to analog in a band-pass digital-analog converter 9. Theoutput signal of the band-pass digital-analog converter 9 is routed witha negative sign to a summing unit 10. The input signal u(t) is amplifiedfor amplitude adjustment in an amplifier 11 and reaches the summing unit10. According to the related art the signal u(t) is also delayed inorder to compensate for the delay to the input signal introduced by thesignal processing device 2 a.

Achievement of runtime compensation based on the example of anapplication shown in FIG. 4 is shown in FIG. 5. A digital filter withthe coefficients α₁=2 and α₂=−1 is used here. As disclosed above, thisfilter has a high level of attenuation at ω=0. The inphase andquadrature components of the low-pass sigma-delta modulator 7 are routedvia a digital mixer 8, multiplied by the coefficient α₁=2 and convertedto an analog signal in a band-pass digital-analog converter 9.

The signal with a negative sign is then routed to a summing unit 10. Theinphase and quadrature components of the low-pass sigma-delta modulator7 are delayed by τ in a delay element 12, combined in a mixer 8 a andmultiplied by the coefficient α₂=−1. After conversion to an analogsignal in a band-pass digital-analog converter 9 a, the signal is routedto the summing unit 10 with a negative sign. The input signal u(t)undergoes an amplitude adjustment by an amplifier 11 but is not delayedas in FIG. 4. The filter downstream from the digital mixer means thatfrequencies in the range ω=2π have a negative group runtime, so thedelay produced by the signal processing device 2 a is compensated forthis frequency range. In other frequency ranges the group runtime ispositive but the output signal is still band-limited, so no additionalrestriction results due to the digital filter.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention.

1. A system for runtime compensation of a runtime difference produced byemulating a high-frequency signal, comprising: a transfer unit whichreceives an input signal and produces an output signal x(t); a signalprocessing unit, which receives the output signal x(t) and emulates thesignal x(t) by producing an emulated signal {circumflex over (x)}(t),the signal processing unit causing the runtime difference; a differenceunit to determine a difference signal between the signals x(t) and{circumflex over (x)}(t); and a filter through which the emulated signal{circumflex over (x)}(t) is routed, the filter being connected betweenthe signal processing unit and the difference unit to filter theemulated signal {circumflex over (x)}(t) before the emulated signal{circumflex over (x)}(t) is fed to the difference unit the filter havinga negative group runtime in a certain frequency range.
 2. The systemaccording to claim 1, further comprising a regulation device, to modifythe emulated signal {circumflex over (x)}(t) so that the differencesignal becomes minimal.
 3. The system according to claim 2, wherein theregulation device is provided at the signal processing device, theregulation device receives the difference signal, and the differencesignal is routed to the signal processing device.
 4. The systemaccording to claim 1, wherein further comprising a signal evaluationunit, which evaluates the difference signal and produces an evaluatedsignal that is routed to the signal processing device.
 5. The systemaccording to claim 1, wherein the input signal is an analog inputsignal, the input signal is supplied to the signal processing unit, andthe input signal controls signal emulation.
 6. The system according toclaim 1, wherein the filter has runtime elements.
 7. The systemaccording to claim 1, wherein the filter is linear.
 8. The systemaccording to claim 1, wherein the filter is an FIR filter.
 9. The systemaccording to claim 1, wherein the filter is an IIR filter.
 10. A systemaccording to claim 1, wherein the signal processing device comprises ananalog to digital converter.
 11. The system according to claim 3,wherein further comprising a signal evaluation unit, which evaluates thedifference signal and produces an evaluated signal that is routed to thesignal processing device.
 12. The system according to claim 11, whereinthe input signal is an analog input signal, the input signal is suppliedto the signal processing unit, and the input signal controls signalemulation.
 13. The system according to claim 12, wherein the filter hasruntime elements.
 14. The system according to claim 13, wherein thefilter is linear.
 15. The system according to claim 14, wherein thefilter is an FIR filter.
 16. The system according to claim 14, whereinthe filter is an IIR filter.
 17. A system according to claim 14, whereinthe signal processing device comprises an analog to digital converter.